Human embryonic stem cells (hESCs) are stem cells derived from the inner cell mass of blastocysts (J. A. Thomson et al, Science 282, 1145-1147, 1998), and exhibit the properties of self-renewal capacity and pluripotency, which is the ability to differentiate into a wide variety of cell types in the human body (K. S. O'Shea et al, Anat Rec 257, 32-41, 1999; A. M. Wobus et al, Preface, Cells Tissues Organs 165, 129-130, 1999). It has been known that these properties of human embryonic stem cells lead to potential applications in the treatment of diseases that result from the destruction or dysfunction of specific cell types, such as diabetes and Parkinson's disease (J. H. Kim et al. Nature 418, 50-56, 2002; S. Gerecht-Niretal, Transpl Immunol 12, 203-209, 2004; Y. Hori et al, Proc Natl Acad Sci USA 99, 16105-16110, 2002). To date, many research groups have made studies on the differentiation of human embryonic stem cells into diverse cell types. There are three general methods for the differentiation of human embryonic stem cells: First, human embryonic stem cells are differentiated into embryoid bodies (Itskovitz-Eldor J et al. Mol Med 6:88-95, 2000). Second, human embryonic stem cells are cultured as a monolayer in the presence of animal serum such as FBS or FCS for spontaneous differentiation (Wang et al. Nature biotech 25, 317-318, 2007). Third, human embryonic stem cells are co-cultured with other differentiated cells (Vodyanik, M. A. et al. Blood 105, 617-626, 2005). In the above differentiation methods, it is adopted that conditions for spontaneous differentiation of human embryonic stem cells are optimized to induce generation of diverse cell types, and the desired cell types are isolated from the diverse differentiated cells. Thus, there are problems in that the efficiency of differentiation into specific cell types is low, and in particular, any use of animal-derived components or sera in culture systems for human embryonic stem cells should be avoided for the research on early human development.
On the other hand, embryonic stem cells are able to differentiate into the ectodermal, mesodermal, and endodermal lineages. Of these, the multipotent stem cells of mesodermal origin during development give rise to the bone, cartilage, tendon, muscle, adipose tissue and vascular endothelium (Minguell et al., Esp. Biol. Med. 226, 507-520, 2001). The hemangioblast would represent a cell population developing from uncommitted mesoderm. Since the mesenchymal stem cells retain a self-renewing property, implantation of these cells in various animal model systems leads to the differentiation of these cells at localized sites and the subsequent regeneration of tissues such as blood vessels and various blood cells. Thus, the mesenchymal stem cells can be used for cell therapy. To yield a sufficient amount of the mesenchymal stem cells for use in cell therapy, a technique to induce the differentiation of embryonic stem cells into mesenchymal stem cells is needed. However, to date, there are no reports on the method of effectively inducing the differentiation of embryonic stem cells into mesenchymal stem cells.
In addition, techniques to induce differentiation of embryonic stem cells into hemangioblasts are as follows: a method of inducing the direct differentiation of embryonic stem cells into endothelial cells by culturing the embryonic stem cells in a medium containing VEGF, bFGF, IGF (insulin-like growth factor) and EGF (epidermal growth factor) (WO 03/040319), a method for generating hematopoietic lineage by culturing embryonic stem cells in a medium containing hematopoietic growth factors selected from SCF (stem cell factor), FLT-3 ligand, IL-3, IL-6 and G-CSF (granulocyte colony stimulating factor) (US Patent publication No. US 2003/0153082), a method for inducing differentiation of human embryoid bodies into hemopoietic stem cells by co-culturing human embryoid bodies with human placenta stromal cells (Korean Patent Application No. 10-2006-0009934), and a method for promoting differentiation of human embryoid bodies to hemopoietic stem cells by co-culturing human embryoid bodies with human bone marrow stromal cells (Korean Patent Application No. 10-2004-0097538). However, there are still no trials that induce differentiation into hemangioblast by regulating the embryonic stem cell signaling pathway.